Higher plant embryogenesis is divided conceptually into two distinct phases: early morphogenic processes that give rise to embryonic cell types, tissues, and organ systems, and late maturation events that allow the fully developed embryo to enter a desiccated and metabolically inactive state. Upon reception of the appropriate signals, the dormant embryo germinates, and seedling development begins. Thus, seed maturation and metabolic quiescence Interrupt the morphogenic processes that occur during embryogenesis and seedling development. This unique form of development underlies, in part, a plant's ability to make seeds, a trait that has conferred significant selective advantages to higher plants. Because lower plants do not make seeds and do not undergo embryo maturation, this bipartite mode of embryogenesis is thought to have resulted from the insertion of mutation events into the higher plant life cycle. Little is known at the mechanistic level about how distinct processes that occur during the morphogenesis and seed maturation phases are coordinated.
The leafy cotyledon1 (LEC1) gene controls many distinct aspects of embryogenesis. The lec1 mutation is pieiotropic, which suggest that LEC1 has several roles in late embryo development. For example, LEC-1 is required for specific aspects of seed maturation, inhibiting premature germination and plays a role in the specification of embryonic organ identity. Finally, LEC1 appears to act only during embryo development. Two other LEG class genes, LEC2 and FUSCA3 (FUS3), are thought to share similar or overlapping functions with LEC1, including the specification of cotyledon identity and the maintenance of maturation. It is unknown how LEG class genes act at the molecular level, but their involvement in many diverse aspects of embryogenesis suggests that these genes encode products that serve as regulators of higher plant embryonic processes. The LEC1-related transcription factors disclosed below all have homology to the maize CAAT-box DNA binding protein subunit B and the Arabidopsis LEC1 protein (WO 9837184-A) and as such may define a new family of LEC1 transcription factors.
Accordingly, the availability of nucleic add sequences encoding all or a portion of these LEG1-related transcription factors would facilitate studies to better understand plant embryoganesis, and provide genetic tools for the manipulation of plant growth.